There are three successive stages of blood formation in the embryo and foatus.
1. Mesoblastic haemopoiesis:-
It is the blood formation and occurs in the first two months of embryonic life. In this case most of the cells are formed outside the embryo. This stage diminished in a human embryo of nine weeks.
2. Hepatic- haemopoiesis:-
This constitutes the see and stage and includes. The splenic and thy-mic blood formation this stage occurs from the end to fifth month.
3. Myeloid haemopoiesis :-
This stage beings at the fifth with the establishment of the presental circulation. In this stage first liver is responsible for the formation of R.B.C's and the bone marrow for the W.B.C's later in the bone marrow take the responsibility of fer the formation of R.B.C's
Posted by: Wasim Javed